This application is based n and claims priority to Japanese Patent Applications No. 2000-080603, filed Mar. 22, 2000, No. 2000-080604, filed Mar. 22, 2000, and No. 2000-080648, filed Mar. 22, 2000, the entire contents of which are hereby expressly incorporated by reference.
1. Field of the Invention
This invention relates to an engine for a watercraft, and particularly to an improved crankshaft bearing and lubrication system of an engine for a watercraft.
2. Description of the Related Art
Personal watercraft have become very popular in recent years. This type of watercraft is quite sporting in nature and carries one or more riders. A relatively small hull of the personal watercraft defines a rider""s area above an engine compartment. An internal combustion engine powers a jet propulsion unit which propels the watercraft. The engine lies within the engine compartment in front of a tunnel formed on the underside of the hull. A jet propulsion unit, which includes an impeller, is placed within the tunnel. The impeller has an impeller shaft driven by the engine. The impeller shaft extends between the engine and the jet propulsion device through a bulkhead of the hull tunnel.
Typically, two-cycle engines are used in personal watercraft because two-cycle engines have a fairly high power to weight ratio. One disadvantage of two-cycle engines, however, is that they produce relatively high emissions. In particular, large amounts of carbon monoxide and hydrocarbons are produced during operation of the engine. When steps are taken to reduce these emissions, other undesirable consequences typically result, such as an increase in weight of the engine, the cost of manufacture, and/or the reduction of power.
It has been suggested that four-cycle engines replace two-cycle engines in personal watercraft. Four-cycle engines typically produce less hydrocarbon emissions than two-cycle engines while still producing a relatively high power output. However, adapting four-cycle engines for use in personal watercraft has its own engineering and technical challenges due to, at least in part, the limited space available within the hull of a personal watercraft.
A four cycle engine utilizes a more complex lubrication system as compared with a two-cycle engine. In a four-cycle engine, a reservoir of oil is held in an oil pan below the crankcase to be available for circulation by an oil pump. One approach to enabling the use of a four-cycle engine in personal watercraft applications is to provide the engine with a dry sump lubrication system. A dry sump system utilizes a shallow reservoir of oil available for the oil pump as compared with the volume of oil in a wet sump system having an oil pan, thus reducing the overall height of the engine.
In accordance with one aspect of the present invention, an internal combustion engine has an engine body which defines at least one combustion chamber. A crankshaft is journaled for rotation at least partially within the engine body. At least one piston cooperates with the engine body to define the combustion chamber. A valvetrain is also provided which is configured to control a flow of air into, and exhaust gas out of, the combustion chamber. A valvetrain drive assembly is configured to transmit energy from the crankshaft to the valvetrain for operating the valvetrain. The engine further comprises a valvetrain drive assembly having a first drive member driven by the crankshaft. A second drive member is also connected to the crankshaft which drives an output shaft. Both the first and second drive members are disposed proximate to a first end of the crankshaft and a bearing is disposed between the first and second drive members.
By providing the bearing between the first and second drive members, the crankshaft can be made more easily. Also, since part of the load is carried by a bearing at one end of the crankshaft, the size of the crankshaft can be reduced. This makes the overall size of the crankshaft smaller and also makes it easier to tune, or balance, for acceptable performance.
According to another aspect of the present invention, an internal combustion engine comprises an engine body defining at least one combustion chamber. A crankshaft is journaled for rotation at least partially within the engine body. The crankshaft has a first and second end, and at least one piston cooperates with the engine body to define the combustion chamber. A drive gear is connected to the first end of the crankshaft. An output shaft assembly is driven by the drive gear. A lubrication system is configured to circulate lubricant through at least one lubricant gallery defined in the engine body. The lubrication system comprises at least one oil pump having an oil pump gear driven by the output shaft assembly.
According to a further aspect of the present invention, an internal combustion engine comprises an engine body defining at least one combustion chamber. A crankshaft is journaled for rotation at least partially within the engine body and includes first and second ends. At least one piston cooperates with the engine body to define the combustion chamber. An output shaft assembly is driven by the crankshaft. A lubrication system is configured to circulate lubricant through at least one lubricant gallery defined in the engine body. The lubrication system comprises at least one lubricant collection passage disposed in the lower portion of the engine body. The lubrication system also comprises an oil pump having an oil pump shaft disposed at an elevation between the output shaft assembly and the lubricant collection passage. The oil pump shaft is offset from the output shaft assembly relative to a vertical plane containing the rotational axis of the output shaft assembly.
Further aspects, features and advantages of this invention will become apparent from the detailed description of the preferred embodiments which follow.